Compressor start and warm-up control system

ABSTRACT

A compressor warm-up control system for load limiting and stall prevention on start-up is presented. The system employs high and low pressure valves, a shut off valve, a check valve, a fixed orifice and interconnecting piping in conjunction with standard compressor suction control and engine speed control. The low pressure valve and fixed orifice combine to limit compressor load and engine speed during a warm-up period.

D United States Patent 91 in] 3,890,063 Spafford June 17, 1975 [54] COMPRESSOR START AND WARM-UP 2.410.824 11/1946 Lamberton 417/25 CONTROL SYSTEM 2.585.168 2/1952 Platts 417/27 2.595.369 5/1952 Re scha ct a1. 417/28 [75] Inventor: Arth Spa fo yoke. ass. 2.646.9[9 7/1953 Bal tholomew........................ 417/21 [73] Assignee: worthingtomCEL lncorporaed, 2.783.936 3/1957 Kistler 417/28 Holyoke. Mass. [22] ed o 6 3 Primary Examiner-William L. Freeh [21] App]. No.: 416,357 [57] ABSTRACT (52] U S C] 417/27 A compressor warm-up control system for load limit- [51] 49/00 ing and stall prevention on start-up is presented. The system employs high and low pressure valves, a shut [58] Field of Search 417, 23,238; Off valve 3 check valve, a fixed orifice and intercom necting piping in conjunction with standard compressor suction control and engine speed control. The low [56] References cued pressure valve and fixed orifice combine to limit com- UNITED STATES PATENTS pressor load and engine speed during a warm-up pe- 2,212.631 8/1940 Baker 417/25 riod. 2,225,854 12/1940 Baker r 4 l l 417/26 2,317,119 4/1943 Stevens 417/26 10 Claims, 1 Drawing Figure S UPPLY PATENTEDJUN 17 I975 1890.063

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PRESSURE AIR SUPPLY REV HlGH

PRESSU VALVE Lu O z 1...! E

COMPRESSOR START AND WARM-UP CONTROL SYSTEM BACKGROUND OF THE INVENTION This invention relates to start and warm-up controls for compressors. More particularly, this invention relates to a pneumatic control system for engine driven positive displacement rotary type air compressor units.

This invention is directed to the problem of controlling start-up and warm-up of rotary driven compressors. Some compressors, such as those having rotors with sliding vanes, come up to speed as the vanes move out to take the load. Machines of this type are not susceptible to overloading the stalling on start-up, and therefore starting controls are not needed. On the other hand, positive displacement engine driven compressors, such as, for example, those of the screw machine type, experience an immediate imposition of the load on start-up as engine speed is increasing to full speed; and this immediate imposition of the load results in a tendency for stalling because the applied load often exceeds the available power. To overcome this problem it is necessary to reduce the initial load. However, at the same time, engine speed must be maintained above idle for proper warm-up and to maintain sufficient air pressure for oil flow purposes.

Most prior art rotary type air compressors employ a pneumatically operated air intake or suction control to limit air receiver (i.e. compressor discharge) pressure and a pneumatically operated engine speed control to set the engine speed in proportion to the air demand. This conventional pneumatic control system uses a single air pressure valve to control signal air flow to the suction and speed controls. This typical control system is quite adequate for normal operation, but it does not solve the start-up problem. The pressure level at which the valve operates to control air intake and engine speed is much too high to prevent the occurrence of stall on start-up. If the valve were set to operate at lower pressure, then normal operating control would be lacking as would be a provision for maintaining engine speed above idle during warm-up.

SUMMARY OF THE INVENTION The above discussed and other problems of the prior art are eliminated or substantially overcome by the start and warm-up control system of the present invention. The present invention employs two air pressure valve, one a standard high pressure valve and the other a start-up low pressure valve, in parallel lines for controlling air intake and engine speed. On start-up, a shut off valve in the line to the low pressure valve is opened to permit air flow to come from compressor discharge to the air intake control. This results in complete or substantially complete termination of air intake at partial load to prevent stalling. This low pressure air is also delivered through an in-line orifice to the engine speed control. The orifice reduces the pressure signal so that the amount of engine speed reduction is limited whereby engine speed is reduced to a level somewhat above idle speed. When it is desired to establish normal control, compressor discharge flow to the low pressure valve is terminated whereby air flow and engine speed are increased. When compressor discharge pressure thereafter reaches a predetermined higher level, the high pressure valve in the parallel control line opens to deliver normal control signals to the engine speed control and the air intake control. A check valve in a line connecting the high pressure valve to the air inlet control permits the high pressure air to flow to the inlet control, but this check valve prevents flow of the low pressure air directly to the engine speed control, thus assuring that the low pressure air must flow through the in-line orifice to encounter the desired pressure reduction.

Accordingly, one object of the present invention is to provide a novel and improved start and warm-up control system for engine driven rotary compressors.

Still another object of the present invention is to provide a novel and improved start and warm-up control for engine driven rotary compressors whereby the problem of stalling on start-up is overcome or significantly reduced.

Still another object of the present invention is to provide a novel and improved start and warm-up control for engine driven rotary compressors wherein the problem of stalling on start-up is alleviated while still maintaining an above-idle warm up speed and an appropriate air pressure level to establish and maintain oil circulation.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a schematic representation of the start and warm-up control system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the single FIGURE of the drawing, suction control unit 10 regulates air intake to the compressor, and engine speed control unit 12 regulates the speed of the engine which drives the compressor. Suction control unit 10 and engine speed control unit 12 are both standard elements presently known and used in the art, and they are shown only in schematic configuration.

Atmospheric air enters suction control unit 10 through intake 14 and flows between valve plate 16 and valve seat 18 to compressor supply line 20 when suction control unit 10 is in the open configuration. Suction created by the intake of the compressor tends to move valve plate 16 to the left to admit the flow of atmospheric air from inlet 14 to supply line 20 when the compressor is rotating. A plunger 22 is held to the left by a main spring 24 grounded on a retainer 26, and a small spring 28 extends between the plunger 22 and valve plate 16. Main spring 24 holds plunger 22 against the right side of diaphragm 30. When an appropriate pressure signal is applied to the left side of diaphragm 30, a rightward force is imposed on plunger 22 which, when the force of spring 24 is overcome, is transmitted via spring 28 to valve plate 16 to drive the valve plate toward or against seat 18 to restrict or terminate air flow.

Engine speed control unit 12 has a linkage arm 32 pivotally connected at one end to pivot point 34, and the other end of link 32 is connected to a linkage arm 36 which goes to the engine throttle. A spring 38 urges link 32 in a clockwise direction, the clockwise direction corresponding to increased throttle opening and increased engine speed. A floating block 40 is attached to a mid-point of link 32, and floating block 40 engages a diaphragm 42. When a pressure signal is applied to the pressure chamber on the right side of diaphragm 42, it results in a leftward force on block 40 and a counterclockwise rotation of link 32 against the force of spring 38. This counterclockwise rotation of link 32 is transmitted to the engine via link 36 to reduce engine speed.

It will be understood that the suction control unit and the speed control unit 12 described hereinabove are typical state of the art elements which are normally operated to reduce or shut off the air supply to the compressor and reduce engine speed from full load to idle when the demand for compressed air decreases and the compressor discharge pressure exceeds a predetermined value. However, the operation of suction control unit 10 and engine speed control unit 12 to meet standard operating conditions does not meet the special problems encountered in start-up and warm-up.

The start-up and warm-up problems are met and overcome in the present invention by the delivery of a sequence of operating signals of different pressure levels to suction control unit 10 and engine speed control unit 12.

Pressurized air for operating control units 10 and 12 is delivered via a supply line 44 from the discharge of the compressor or from the air receiver (not shown). Supply line 44 divides into two parallel branch lines 46 and 48. Branch line 46 contains a shut off valve 50 and a low pressure responsive valve 52 downstream of shut off valve 50. A high pressure operated valve 54 is in line 48. During engine start-up, shut off valve 50 is opened to permit air under pressure to reach valve 52. When the pressure in line 46 reaches the value set for opening valve 52, air under pressure then flows to line 56 and is delivered to the left side of diaphragm 30 to load diaphragm 30 to the right to shutdown the flow of air through suction control unit 10. Line 56 has a variable bleed orifice 58 to permit control of the rate of pressure build-up against diaphragm 30.

The pressurized air in line 46 also flows through line 60 and through a restriction 62 in line 60 to line 64 which leads to the pressure chamber in unit 12 on the right side of diaphragm 42. A bleed orifice 66 also communicates with this pressure chamber and hence pro vides a regulated bleed path to atmosphere. The air flowing through restriction 62 experiences a pressure drop because of the combined action of restriction 62 and bleed orifice 66. Accordingly, the pressure imposed on the right side of diaphragm 42 is reduced or stepped down pressure with respect to that in line 46 and that which is imposed on diaphragm 30. This reduced pressure results in an intermediate counterclockwise rotation of link 40 whereby engine speed is reduced below the full load figure but not reduced all the way to idle speed. This stepped down pressure signal in effect, makes the engine speed control operate as if the pressure discharge pressure were at a lower level than actually exists so that the engine speed is not reduced all the way to idle.

After start-up and an appropriate warm-up have been completed, the control system is converted to normal control configuration merely by closing shut off valve 50. The closing of shut off valve 50 removes the pressure signals in line 56 and 64, thus unloading the diaphragms in the suction control unit and the speed control unit so that the suction control unit returns to a full open position and the speed control unit returns to its full load speed position. When compressor discharge pressure thereafter reaches the value necessary to open high pressure valve 54, a pressure signal is again delivered to line 64 to impose a load on diaphragm 42 in speed control unit 12. However, this is now a higher pressure signal than previously imposed on diaphragm 42, and link 32 is rotated counterclockwise by an amount sufficient to reduce engine speed to idle. The high pressure in line 48 which has opened valve 54 also flows through an interconnecting line 68 to line 56 where it is then delivered to load diaphragm 30 to the right to close the suction control unit and terminate the flow of intake air to the compressor. Line 68 contains a check valve 70 which only permits air to flow from left to right as viewed in the drawing. It will be observed that the high pressure air in line 48 also flows in a reverse direction through line 60 to line 56. However, interconnecting line 68 and check valve 70 are required for proper operation of this control system in the low pressure operating mode. That is, when valve 52 is open to deliver the low pressure signals on start-up, check valve 70 prevents the low pressure air from bypassing restriction 62 and thus insures that only a stepped down pressure signal is delivered to diaphragm 42. This interconnecting line 68 also insures that the full level of air pressure in line 48 will be delivered to line 56 when valve 54 is open without encountering the pressure drop which would otherwise occur if the air had to flow in the reverse direction through orifice 62 in line 60 to get to line 56.

High pressure valve 54 corresponds to the single valve known in the art for pneumatically controlling the suction control unit and the engine speed control unit. The present invention provides a dual level operating system wherein the regular control functions without impairment while significantly alleviating the serious problem of stalling on engine start-up. Furthermore, an adequate supply of makeup air is maintained to the compressor to provide for pressurization of the oil circulation system in the compressor and associated machinery since suction control unit 10 can cycle between a fully closed and partly open position if the compressor discharge pressure falls below the pressure needed to keep valve 52 fully open during warm-up.

While a preferred embodiment has been disclosed various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.

What is claimed is:

l. A start and warm-up control for an engine driven compressor including:

means for controlling the delivery of gas to a compressor;

means for controlling the speed of an engine driving the compressor;

first supply line means connected to said gas delivery control means and to said speed control means, said first supply line means including first pressure responsive means responsive to a first level of compressor discharge pressure during a warmup period for delivering first signal pressure to both said gas delivery control means and said speed control means for controlling gas flow to the compressor and for reducing engine speed to a first control valve below full speed but above idle speed, said first supply line means including pressure reducing means for reducing the pressure of said first signal to said speed control means below the pressure to said gas delivery control means; and

second supply line means connected to said speed control means and to said gas delivery control means, said second supply line means including second pressure responsive means responsive to a second level of compressor discharge pressure during normal operation for delivering a signal pressure to both said gas delivery control means and said speed control means for controlling gas flow to the compressor and reducing engine speed to a second control value, said second level of compressor discharge pressure being higher than said first level of compressor discharge pressure and said second control value of engine speed being lower than said first control value of engine speed, said first and second supply line means being interconnected at a point downstream of said pressure reducing means in said first supply line means.

2. A start and warm-up control as in claim 1 including:

flow control means for selectively initiating or terminating delivery of compressor discharge gas to said first pressure responsive means.

3. A start and warm-up control as in claim 1 wherein:

said first pressure responsive means is a valve which opens at said first level of compressor discharge pressure to admit signal pressure to said gas delivery control means and to said speed control means; and

said second pressure responsive means is a valve which opens at said second level of compressor dis charge pressure to admit signal pressure to said gas delivery control means and to said speed control means.

4. A start and warm-up control as in claim 1 wherein:

said pressure reducing means includes orifice means in said first supply line means, and bleed means communicating with said first supply line whereby said speed control means operates contemporaneously with said gas delivery control means when said first level of compressor discharge pressure is reached but said speed control means operates as if the compressor discharge pressure were lower than said first level.

5. A start and warm-up control as in claim 4 wherein:

said second supply means includes a second supply line part interconnecting with said first supply line means upstream of said orifice means; and

flow direction control means in said interconnecting part for permitting flow in said interconnecting part only from said second valve means to said gas delivery control means.

6. A start and warm-up control for an engine driven compressor including:

means for controlling the delivery of gas to a compressor;

means for controlling the speed of an engine driving the compressor;

first conduit means for delivering gas under pressure from the discharge of a compressor to said gas delivery control means and to said speed control means;

first pressure responsive valve means in said first conduit means responsive to a first pressure level to permit the flow of gas in said first conduit means;

reducing means in said first conduit means for reducing the pressure of gas delivered to said speed control means below the pressure of gas delivered to said gas delivery control means;

second conduit means for delivering gas under pressure from the discharge of a compressor to said speed control means and said gas delivery control means, at least part of said second conduit means being in parallel with said first conduit means;

second pressure responsive valve means in said second conduit means responsive to a second pressure level to permit the flow of gas in said second conduit means, said second pressure level being higher than said first pressure level;

said first and second conduit means being interconnected at a point downstream of said reducing means in said first conduit means; and

flow control means for selectively initiating or terminating delivery of gas under pressure from the discharge of a compressor to said first valve means.

7. A start and warm-up control as in claim 6 wherein:

said first conduit means includes a first segment connected to said air delivery control means and a second segment interconnecting said first segment to said speed control means; and wherein said second conduit means includes a first segment connected to said speed control means and a second segment interconnecting said first segment to said air delivery control means.

8. A start and warm-up control as in claim 7 wherein:

said reducing means in said first conduit means is orifice means in said second interconnecting segment of said first conduit communicating with bleed means.

9. A start and warm-up control as in claim 8 including:

check valve means in said second interconnecting segment of said second conduit means to permit flow in said second interconnecting segment only to said air delivery control means.

10. A start and warm-up control as in claim 9 wherein:

said first and second conduit means are connected to a common gas supply conduit.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,390,0 3 DATED l June 17, 1975 INVENTOR(S) Arthur R. Spafford It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown beiow;

Column 1, line 14, after "overloading" change "the" to --and-- Column 1, line 49, change "valve" (first occurrence) to --valves-- Column 4, line 66 (Claim 1) change "valve" to --value- Signed and Sealed this sixteenth D ay Of September 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parents and Tradvmurkx 

1. A start and warm-up control for an engine driven compressor including: means for controlling the delivery of gas to a compressor; means for controlling the speed of an engine driving the compressor; first supply line means connected to said gas delivery control means and to said speed control means, said first supply line means including first pressure responsive means responsive to a first level of compressor discharge pressure during a warmup period for delivering first signal pressure to both said gas delivery control means and said speed control means for controlling gas flow to the compressor and for reducing engine speed to a first control valve below full speed but above idle speed, said first supply line means including pressure reducing means for reducing the pressure of said first signal to said speed control means below the pressure to said gas delivery control means; and second supply line means connected to said speed control means and to said gas delivery control means, said second supply line means including second pressure responsive means responsive to a second level of compressor discharge pressure during normal operation for delivering a signal pressure to both said gas delivery control means and said speed control means for controlling gas flow to the compressor and reducing engine speed to a second control value, said second level of compressor discharge pressure being higher than said first level of compressor discharge pressure and said second control value of engine speed being lower than said first control value of engine speed, said first and second supply line means being interconnected at a point downstream of said pressure reducing means in said first supply line means.
 2. A start and warm-up control as in claim 1 including: flow control means for selectively initiating or terminating delivery of compressor discharge gas to said first pressure responsive means.
 3. A start and warm-up control as in claim 1 wherein: said first pressure responsive means is a valve which opens at said first level of compressor discharge pressure to admit signal pressure to said gas delivery control means and to said speed control means; and said second pressure responsive means is a valve which opens at said second level of compressor discharge pressure to admit signal pressure to said gas dElivery control means and to said speed control means.
 4. A start and warm-up control as in claim 1 wherein: said pressure reducing means includes orifice means in said first supply line means, and bleed means communicating with said first supply line whereby said speed control means operates contemporaneously with said gas delivery control means when said first level of compressor discharge pressure is reached but said speed control means operates as if the compressor discharge pressure were lower than said first level.
 5. A start and warm-up control as in claim 4 wherein: said second supply means includes a second supply line part interconnecting with said first supply line means upstream of said orifice means; and flow direction control means in said interconnecting part for permitting flow in said interconnecting part only from said second valve means to said gas delivery control means.
 6. A start and warm-up control for an engine driven compressor including: means for controlling the delivery of gas to a compressor; means for controlling the speed of an engine driving the compressor; first conduit means for delivering gas under pressure from the discharge of a compressor to said gas delivery control means and to said speed control means; first pressure responsive valve means in said first conduit means responsive to a first pressure level to permit the flow of gas in said first conduit means; reducing means in said first conduit means for reducing the pressure of gas delivered to said speed control means below the pressure of gas delivered to said gas delivery control means; second conduit means for delivering gas under pressure from the discharge of a compressor to said speed control means and said gas delivery control means, at least part of said second conduit means being in parallel with said first conduit means; second pressure responsive valve means in said second conduit means responsive to a second pressure level to permit the flow of gas in said second conduit means, said second pressure level being higher than said first pressure level; said first and second conduit means being interconnected at a point downstream of said reducing means in said first conduit means; and flow control means for selectively initiating or terminating delivery of gas under pressure from the discharge of a compressor to said first valve means.
 7. A start and warm-up control as in claim 6 wherein: said first conduit means includes a first segment connected to said air delivery control means and a second segment interconnecting said first segment to said speed control means; and wherein said second conduit means includes a first segment connected to said speed control means and a second segment interconnecting said first segment to said air delivery control means.
 8. A start and warm-up control as in claim 7 wherein: said reducing means in said first conduit means is orifice means in said second interconnecting segment of said first conduit communicating with bleed means.
 9. A start and warm-up control as in claim 8 including: check valve means in said second interconnecting segment of said second conduit means to permit flow in said second interconnecting segment only to said air delivery control means.
 10. A start and warm-up control as in claim 9 wherein: said first and second conduit means are connected to a common gas supply conduit. 